Wireless LAN systems are generally known in the art. For example, one is described in IEEE 802.11 Working Document, 11/92-39, entitled "Medium Access Control Protocol for Wireless LANs". This document discloses a wireless LAN system using a frequency hopping/spread spectrum system for changing each carrier frequency based on the same hopping series and hopping cycle or period defined at each cell. In other words, according to this system, the carrier frequencies are hopped in a frame unit.